This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-150253, filed May 22, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to copper plating and, more particularly, to an electroplating apparatus and electroplating method of performing single wafer processing for semiconductor substrates and the like.
Electroplating of copper which has been often used in plating industries for a long time is recently attracting attention as a multilayered wiring process for semiconductors. This is so because copper having low resistivity is beginning to be used as a multilayered wiring material of semiconductors. In addition, film formation by plating is superior in step coverage and hence well matches a wiring formation process (damascene process). Also, film formation by plating is possible at higher speed and lower cost than film formation by, e.g., sputtering. These are other reasons of the introduction of the plating process.
In copper plating, however, caution should be exercised on a thin black film called a xe2x80x9cblack filmxe2x80x9d formed on the surface of an anode. This black film is presumably a compound of oxygen or chlorine contained in a plating liquid and copper or phosphorus contained in phosphorus containing copper as an anode material. When a substrate to be processed is plated, copper is formed on the substrate as a cathode and a black film is formed on an anode by application of electricity.
This black film is stable as long as electricity is supplied to a plating liquid. However, when electricity is turned off or the anode is pulled up from the plating liquid, the black film is lost as it is removed from the anode or dissolved in the plating liquid. If the black film is partly lost on the surface of the anode, the uniformity of film formation on the wafer as a substrate to be processed significantly lowers, or a precipitation is formed on the film surface.
In practice, therefore, if the time during which an electroplating apparatus is unused exceeds a predetermined time, electricity is applied by using a dummy wafer to intentionally form a black film. This is called xe2x80x9canode burn-inxe2x80x9d. This anode burn-in is indispensable to stably obtain performance (e.g., filling performance and film thickness uniformity) of copper plating.
Furthermore, even on an anode such as an indissoluble anode on which no black film is formed, oxidation of the anode occurs owing to application of an electric current. This makes the state of the anode surface when electricity is applied different from that when the anode is left to stand for a long time period. Therefore, anode burn-in is necessary regardless of the presence/absence of a black film.
Accordingly, after plating to a wafer to be processed is stopped for a predetermined time, anode burn-in to a dummy wafer must be performed prior to wafer plating in the next process. This significantly lowers the utilization efficiency of the electroplating apparatus.
An example of anode burn-in and its problem will be described below by taking a cup type electroplating apparatus most extensively used in the semiconductor industries as an example. FIG. 1 is a sectional view of the cup type electroplating apparatus whose main purpose is copper plating. As shown in FIG. 1, this apparatus comprises a plating liquid 2 filled and circulated in a cup 1, an anode 3 placed in the cup 1, an electrode 5 for giving a negative potential to the surface of a wafer 4 facing the anode 3, a seal 6 for preventing the plating liquid 2 from contacting the electrode 5, and a power supply 7 for supplying an electric current to the wafer 4 and the anode 3.
The plating liquid is usually an aqueous solution mixture of copper sulfate, sulfuric acid, and hydrochloric acid. When the wafer 4 is completely processed and retracted, no electric current flows to the anode 3 any longer. The anode 3 is exposed to the plating liquid 2 in this state. Alternatively, the anode 3 is exposed to the atmosphere if the plating liquid 2 is discharged from the cup 1. In either case, a black film formed on the surface of the anode 3 changes in properties with time. Hence, the manufacturer of the apparatus recommends maintenance, e.g., as shown in FIGS. 2 and 3.
As shown in FIGS. 2 and 3, when the electroplating apparatus is set in a standby state after plating is completed, a preparation time before plating becomes possible and is needed in order to resume plating. That is, the actual wafer processing of the electroplating apparatus is very wasteful in Large Scale Integration (LSI) factories, and this raises the LSI process cost. In particular, the multilayered wiring step is in the latter half of the LSI fabrication process. In a factory, therefore, predetermined numbers of wafers are anode but large numbers of wafers are intermittently supplied. Accordingly, anode burn-in explained above sometimes occupies nearly ⅓ of the operation time of the electroplating apparatus. This is a serious problem in the LSI fabrication process.
It is an object of the present invention to provide an electroplating apparatus and electroplating method capable of improving the throughput by reducing the anode burn-in time.
To achieve the above object, an electroplating apparatus according to the first aspect of the present invention comprises a holder configured to hold a substrate to be processed serving as a cathode, a dummy cathode placed in a position different from the holder, an anode capable of facing, substantially face to face, both a surface to be plated of the substrate held by the holder and the dummy cathode, a moving mechanism configured to move the anode between the substrate holder and the dummy electrode, and a power supply connected between the dummy cathode and the anode to supply an electric current between the anode and the dummy cathode via an electrolytic agent filled between the dummy cathode and the anode.
An electroplating apparatus according to the second aspect of the present invention comprises a cup to be filled with an electrolytic agent, an anode placed on a bottom of the cup, a holder for holding a substrate to be processed in an upper portion of the cup, such that a surface to be plated of the substrate faces the anode, a dummy cathode capable of moving, as needed, to a position between the anode and the substrate, a moving mechanism for retracting the dummy cathode when the substrate is to be plated, and opposing the dummy cathode substantially face to face to the anode when plating of the substrate is stopped, and a power supply connected between the dummy cathode and the anode.
An electroplating method according to the third aspect of the present invention comprises the steps of preparing a dummy cathode, opposing a plate-like anode substantially face to face and parallel to the dummy cathode via an electrolytic agent, with no electricity applied, supplying an electric current between the anode and the dummy cathode after the step of opposing the anode to the dummy cathode, and opposing a substrate to be processed serving as a cathode to the anode via an electrolytic agent and forming a plating film on the substrate, after the step of supplying an electric current between the anode and the dummy cathode.
In the present invention, changes in properties of a black film are suppressed by filling an electrolytic agent into a portion between an anode and a dummy cathode which is opposite substantially face to face and parallel to the anode, and supplying an electric current to this portion. Since extra anode burn-in is unnecessary, the throughput improves.
The effect of the present invention is large in copper plating in which the formation of a black film is significant. The consumption power and dissolution of the anode can be reduced by applying an electric current to the anode immediately before resumption of plating or by intermittently applying this electric current. In particular, the film formation characteristics of plating to a substrate to be processed can be maximally stabilized by applying the electric current to the anode immediately before the substrate is plated.
When both the dummy cathode and the anode are substantially flat plates and the apparatus comprises a mechanism capable of maintaining these cathode and anode parallel to each other, the density of an electric current flowing through the anode becomes uniform, so a uniform black film can be formed on the anode. This can realize a uniform plating film growth rate and uniform film formation characteristics over the entire surface of a substrate to be processed. When phosphorus containing copper is used as the anode, the formation of a black film occurs stably, and this makes the effect of the present invention remarkable.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.